const_lookup.rb

Object.const_defined? :Integer
#=> true

integer.rb

class Integer
  #...
end

def Integer(value)
  #...
end

method_lookup.rb

Object.private_method_defined? :Integer
#=> true

python_class_is_callable.py

class MyClass:
    def __init__(self, value):
        self.value = value

my_class = MyClass(1) # We are calling the class to get
                      # an instance, instead of
                      # MyClass.new(1) in Ruby

ruby_class_looks_callable.rb

Integer.class
#=> Class

Integer(1)
#=> 1